The present disclosure relates to a detection apparatus, a power supply system, and a method of controlling a detection apparatus. More specifically, the present disclosure relates to a detection apparatus that detects a foreign object in a magnetic field, a power supply system, and a method of controlling a detection apparatus.
In recent years, public attention has been drawn to power supply systems in which power is supplied to CE (Consumer Electronics) devices, such as a mobile phone, a mobile music player, and the like in an electrically non-contact manner. These power supply systems are referred to as non-contact power supply systems, non-contact power transmission systems, wireless power supply systems, or the like. With these systems, it is possible to charge secondary devices by a simple method, for example placing a secondary device, such as an electronic device, or the like on a primary device, such as a power supply device, or the like. That is to say, a terminal connection becomes unnecessary between an electronic device and a power supply device.
As a method of performing non-contact power supply in this manner, an electromagnetic induction method has been familiar. Also, recently, a non-contact power supply system using a method called a magnetic field resonance method (or a magnetic resonance method) with the use of resonance phenomena has attracted attention.
A non-contact power supply system using the magnetic field resonance method has an advantage in that it is possible to perform power transmission on a principle of resonance phenomena between devices that are disposed more apart from each other than in the case of the electromagnetic induction method. Also, the non-contact power supply system using the magnetic field resonance method has an advantage in that even if axis alignment between a power supply coil of a power supply source and a power reception coil of a power supply destination is deteriorated in some degree, power transmission efficiency (that is to say, power supply efficiency) is not decreased so much.
However, both of the magnetic field resonance method and the electromagnetic induction method are non-contact power supply systems using magnetic coupling between the power supply coil of the power supply source and the power reception coil of the power supply destination.
Incidentally, one of important elements of a non-contact power supply system is a countermeasure against heat generation by a foreign object, such as metal, a magnetic body, a magnet, and the like that might generate heat through lines of magnetic force. In a non-contact power supply system using an electromagnetic induction method or a magnetic field resonance method, if a foreign object is put into a gap between a power supply coil and a power reception coil, the foreign object might generate heat by lines of magnetic force passing through the foreign object. This heat generation of the foreign object is caused by an eddy current loss generated in a metallic foreign object by the passage of lines of magnetic force through the metallic foreign object, a hysteresis loss generated in a foreign magnetic body, and the like by the passage of lines of magnetic force through a foreign magnetic body, a foreign magnet, or the like.
Heat generation by a foreign object might cause malfunction or damage of a power supply device and an electronic device, and the like. Accordingly, the prevention of heat generation by a foreign object is said to be a major task for a non-contact power supply system.
As a countermeasure against the heat generation, a method of adding a temperature sensor in order to detect heat generation by a foreign object is provided. However, in this method, a foreign object that has already generated heat is to be detected, and thus this method is difficult to become a fundamental countermeasure against heat generation by a foreign object. That is to say, it is desirable to provide a method of detecting a foreign object that might generate heat through lines of magnetic force before the foreign object actually generates much heat.
Thus, a proposal has been made of a method of checking changes in electrical parameters (a current, a voltage, and the like) when there is a metallic foreign object inserted between a power supply apparatus and a power reception apparatus, and determining the presence or absence of the metallic foreign object. By such a method, it is possible to detect existence of a foreign object before the foreign object generates much heat. Specifically, a proposal has been made of a method of detecting a metallic foreign object by changes in amplitude and phase at the time of communication between the power supply apparatus and the power reception apparatus (for example, refer to Japanese Unexamined Patent Application Publication No. 2008-206231). Also, a proposal has been made of a method of detecting a metallic foreign object by an eddy current loss (for example, refer to Japanese Unexamined Patent Application Publication No. 2001-275280).